Method of handling liquid non-ferrous metals with refractory material

ABSTRACT

A method of handling liquid non-ferrous metals in which the liquid metal is treated while coming into contact with a solid refractory material. The invention is characterised in that the solid material is Ti 3 SiC 2 . According to one preferred embodiment, the liquid material is aluminium or aluminium alloys.

[0001] The present invention relates to a method of handling liquid non-ferrous metals, and more specifically to the solid material with which the liquid material comes into contact.

[0002] There is a need for refractory material that can resist the aggressive conditions that occur when the material comes into contact with liquid non-ferrous metals, such as aluminium. Among other things, this need is due to the increasing use of aluminium in vehicle parts, such as chassis and cast engine parts. Material that shall be used in direct contact with liquid aluminium must possess good corrosion properties and good erosion properties and also have a high resistance to oxidation at high temperatures and against thermal shocks, and shall also have high impact resistance and high strength and hardness. The material shall also be capable of being easily worked into complex shapes at a competitive cost.

[0003] The aluminium industry uses at present silicon aluminium oxynitride, SIALON, despite its high manufacturing costs. One drawback with SIALON, however, is that it is brittle and therefore expensive to work.

[0004] SiC and Si3N4 are materials that have also been evaluated in contact with liquid aluminium. It was found that Si dissolved into liquid aluminium in both cases. Si3N4 was found to have the best resistance to corrosion when produced by hot isostatic pressing (HIP) of reaction-bound Si3N4 (HIPRBSN).

[0005] A dense protective layer was formed from AIN. SiC has been found to have low corrosion resistance when the material is manufactured by using silicon metal as a binding phase. Brittleness, difficulties in mechanical working, poor resistance against thermal shocks, low impact resistance, and reactions with liquid aluminium are among the drawbacks exhibited by SiC when used with liquid aluminium.

[0006] Generally speaking, the high affinity of Al to Si and the high solubility of Si in Al normally results in Si dissolving in liquid aluminium.

[0007] Some metallic materials, such as cast iron, have normally been used in conjunction with liquid aluminium, because these metals are inexpensive, have high mechanical strength and resist thermal shocks. Cast iron protective pipes, however, are wetted by liquid aluminium, resulting in dissolving of the material with subsequent contamination of the melt with undesirable iron particles.

[0008] The aforesaid problems are solved by the present invention.

[0009] The present invention thus relates to a method of handling liquid non-ferrous metals, in which the liquid metal is treated as it comes into contact with a solid refractory material, said method being characterised in that the solid material is Ti₃SiC₂.

[0010] It has surprisingly and unexpectedly been found that this material is stable in liquid aluminium. It has been found that when in contact with liquid aluminium there is formed on the surface of the material a reaction zone which produces a layer that passivates the outer surface of said material and which prevents chemical corrosion in all essentials.

[0011] The material has therefore been found excellent in respect of handling liquid aluminium and aluminium alloys.

[0012] The material Ti₃SiC₂ has a unique combination of properties that render it suitable for high temperature applications. It has very good working properties, which enable complicated shapes to be produced. The material is also insensitive to thermal shocks. Ti₃SiC₂ is also a material that has high impact resistance and an equilibrium temperature between brittle and tough material of about 1200° C. The thermal conductivity of the material is about 37 W/mK at room temperature. The material can be produced by conventional methods of producing ceramic materials, such as extrusion, cold isostatic pressing (CIPing), casting and packing by pressureless sintering, or by hot isostatic pressing (HIP). Minor fractions of TiC, SiC and TiSi₂ may be present in the finished material. The above mentioned treatment of the liquid material includes melting, retaining, such as when alloying, transportation, filtration, such as when degassing and purifying the material, or casting of the liquid material.

[0013] Aluminium has been mentioned above. According to a preferred embodiment, the liquid material is magnesium or magnesium alloys instead.

[0014] It is also conceivable to use successfully said material for other metals or metal alloys that have a relatively low melting point. Zinc, copper, tin and lead or their alloys are primarily intended in this respect.

[0015] The present invention is therefore not restricted to liquid material in the form of aluminium or magnesium, but can be applied with respect to other materials in which the material Ti₃SiC₂ is stable.

[0016] It will therefore be understood that the present invention is not restricted to the aforedescribed embodiments thereof but variations can be made within the scope of the accompanying Claims. 

1. A method of handling liquid non-ferrous metals, in which the liquid metal is treated while coming into contact with a solid refractory material, characterised in that the solid material is Ti₃SiC₂.
 2. A method according to claim 1, characterised in that the liquid material is aluminium or aluminium alloys.
 3. A method according to claim 1 or 2, characterised in that the liquid material is magnesium or magnesium alloys.
 4. A method according to claim 1 or 2, characterised in that said treatment includes melting, retaining, transporting, filtering or casting the liquid material. 